It's automated ContentID flagging, right? Classical music is a problem because different (copyrighted) performances have very similar music fingerprints. If you tune the music fingerprinting to distinguish between different performances of the same piece by Chopin, you will probably get false negatives if someone uploads a video with a Taylor Swift song that has some background noise added or slightly sped up or slowed down.

False negatives are a problem, because big content rights holders get upset. False positives rarely matter.

Not to ignore cases of manual copyright flagging abuse, but that's usually done for vindictive or careless reasons; there shouldn't be any reason for anyone to flag a video of someone performing an old classical piece.